Semiconductor device

ABSTRACT

A semiconductor device of the present invention includes a semiconductor layer, a plurality of gate trenches formed in the semiconductor layer, a gate electrode filled via a gate insulating film in the plurality of gate trenches, an n + -type emitter region, a p-type base region, and an n − -type drift region disposed, lateral to each gate trench, in order in a depth direction of the gate trench from a front surface side of the semiconductor layer, a p + -type collector region disposed on a back surface side of the semiconductor layer with respect to the n − -type drift region, an emitter trench formed between the plurality of gate trenches adjacent to each other, and a buried electrode filled via an insulating film in the emitter trench, and electrically connected with the n + -type emitter region, and the emitter trench is disposed at an interval of 2 μm or less via an n − -type drift region with the gate trench.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 13/969,677,filed on Aug. 19, 2013. Furthermore, this application claims the benefitof priority of Japanese applications 2012-182169, filed on Aug. 21,2012, 2012-182168, filed on Aug. 21, 2012, and 2013-167477, filed onAug. 12, 2013. The disclosures of these prior U.S. and Japaneseapplications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a semiconductor device including IGBTs(Insulated Gate Bipolar Transistors).

BACKGROUND ART

Conventionally, a trench-type IGBT having a high saturation voltageV_(CE)(sat) and short-circuit capacity between the collector and emitterhas a p-type floating region. The p-type floating region is generallyformed in a diffused manner in a drift layer so as to contact a gatejunction trench. The drift layer is an epitaxial wafer or a pulled-upwafer having a resistance value comparable thereto.

SUMMARY OF INVENTION

However, the conventional structure has a high stray capacitance in ajunction region between the gate junction trench and p-type floatingregion, and thus has a problem that operating noise and on-operationloss due to said stray capacitance occur when switched ON. Therefore, ithas been difficult to establish low-noise and low-loss characteristics.

It is an object of the present invention to provide a semiconductordevice including IGBTs capable of reducing generation of noise andswitching loss at switching operation, and further capable ofmaintaining withstand voltage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic plan view of a semiconductor device according to afirst embodiment of the present invention.

FIG. 2 is a sectional view from a section II-II of FIG. 1.

FIG. 3 is a sectional view from a section III-III of FIG. 1.

FIGS. 4( a) and (b) are views for explaining an internal structure ofthe semiconductor device of FIG. 1, wherein FIG. 4( a) shows aperspective view, and FIG. 4( b) shows a plan view.

FIG. 5 is a schematic sectional view of a semiconductor device accordingto a second embodiment of the present invention.

FIG. 6A is a view for explaining a manufacturing step of thesemiconductor device of FIG. 5.

FIG. 6B is a view showing a following step of FIG. 6A.

FIG. 6C is a view showing a following step of FIG. 6B.

FIG. 6D is a view showing a following step of FIG. 6C.

FIG. 6E is a view showing a following step of FIG. 6D.

FIG. 6F is a view showing a following step of FIG. 6E.

FIG. 6G is a view showing a following step of FIG. 6F.

FIG. 7 is a schematic sectional view of a semiconductor device accordingto a third embodiment of the present invention.

FIG. 8 is a perspective view for explaining an internal structure of thesemiconductor device of FIG. 7.

FIG. 9 is a schematic sectional view of a semiconductor device accordingto a fourth embodiment of the present invention.

FIG. 10 is a schematic sectional view of a semiconductor deviceaccording to a fifth embodiment of the present invention.

FIG. 11 is a schematic sectional view of a semiconductor deviceaccording to a sixth embodiment of the present invention.

FIG. 12 is an enlarged view of a part enclosed by a broken line of FIG.11.

FIG. 13A is a view for explaining a manufacturing step of thesemiconductor device of FIG. 12.

FIG. 13B is a view showing a following step of FIG. 13A.

FIG. 13C is a view showing a following step of FIG. 13B.

FIG. 13D is a view showing a following step of FIG. 13C.

FIG. 13E is a view showing a following step of FIG. 13D.

FIG. 13F is a view showing a following step of FIG. 13E.

FIG. 13G is a view showing a following step of FIG. 13F.

FIG. 13H is a view showing a following step of FIG. 13G.

FIG. 13I is a view showing a following step of FIG. 13H.

FIG. 13J is a view showing a following step of FIG. 13I.

FIG. 13K is a view showing a following step of FIG. 13J.

FIG. 14 is a schematic sectional view of a semiconductor deviceaccording to a seventh embodiment of the present invention.

FIG. 15 is an enlarged view of a part enclosed by a broken line of FIG.14.

FIG. 16 is a graph showing a relationship between the trench intervaland withstand voltage.

FIG. 17 is a graph showing V_(CE)-I_(Cf) characteristics of devices.

DESCRIPTION OF EMBODIMENTS

A semiconductor device of the present invention includes a semiconductorlayer, a plurality of gate trenches formed in the semiconductor layer, agate electrode filled via a gate insulating film in the plurality ofgate trenches, an n⁺-type emitter region, a p-type base region, and ann⁻-type drift region disposed, lateral to each gate trench, in order ina depth direction of the gate trench from a front surface side of thesemiconductor layer, a p⁺-type collector region disposed on a backsurface side of the semiconductor layer with respect to the n⁻-typedrift region, an emitter trench formed between the plurality of gatetrenches adjacent to each other, and a buried electrode filled via aninsulating film in the emitter trench, electrically connected with then⁺-type emitter region, and the emitter trench is disposed at aninterval of 2 μm or less via an n⁻-type drift region with the gatetrench.

According to this arrangement, the gate trench filled with the gateelectrode (hereinafter, referred to as a “gate junction trench”) joinsthe n⁻-type drift region. Therefore, even when there is formed a p-typefloating region in the semiconductor layer, junction between said p-typefloating region and the gate junction trench can be prevented. A straycapacitance between the gate junction trench and the p-type floatingregion can thereby be eliminated. On the other hand, the n⁻-type driftregion that joins the gate junction trench is to be grounded togetherwith the p⁺-type collector region. Therefore, at switching operation, acapacitance change between the gate junction trench and the n⁻-typedrift region is stabilized, so that noise does not easily occur. As aresult thereof, generation of noise and switching loss at switchingoperation can be reduced.

Also, because the interval between the emitter trench filled with theburied electrode (hereinafter, referred to as an “emitter junctiontrench”) and the gate junction trench is 2 μm or less, withstand voltagecan also be satisfactory maintained.

In addition, a p-type floating region may either be formed or not beformed in the semiconductor layer. However, when a p-type floatingregion is formed in the semiconductor layer where the emitter trench isformed in plural numbers, it is preferable that said p-type floatingregion is formed between the plurality of emitter trenches. That is, itis preferable that a p-type floating region is formed within a regionsandwiched by emitter junction trenches closest to the gate junctiontrenches.

The p-type floating region may be formed at the same depth as that ofthe p-type base region. In this case, because the p-type floating regionmay be formed by the same step as that for the p-type base region, themanufacturing process can be simplified.

On the other hand, the p-type floating region may be formed deeper thanthe p-type base region. In this case, the p-type floating regionpreferably includes an overlap portion that goes around to a lower sideof an emitter trench closest to the gate trench out of the plurality ofemitter trenches.

According to this arrangement, because the p-type floating region(overlap portion) is formed up to a bottom portion of the emitterjunction trench, a collector-emitter voltage to be loaded on the emitterjunction trench at switching-off operation can be relieved. Therefore, adevice breakdown can be prevented against a steep voltage change(dv/dt).

Also, because withstand voltage can be increased by the p-type floatingregion that is deeper than the p-type base region, while the p-type baseregion may be shallow, the channel length can also be reduced tosuppress a rise in ON-voltage by appropriately designing the depth ofthe p-type base region.

The overlap portion preferably has an end portion positioned on a sidecloser to the gate trench with respect to a center in a width directionof the emitter trench.

According to this arrangement, a collector-emitter voltage to be appliedto the emitter junction trench can be more satisfactorily relieved.

Also, it is preferable that the semiconductor device includes an activeregion set on the semiconductor layer and a non-active region adjacentto the active region, and a contact portion disposed, in the non-activeregion, on the semiconductor layer so as to extend across the buriedelectrodes filled in the plurality of emitter trenches, for collectivelyconnecting to the plurality of buried electrodes.

According to this arrangement, disposing the contact portion in thenon-active region allows forming a relatively thick insulating film onthe front surface of the semiconductor layer in the active region.Therefore, insulation breakdown in the active region can be prevented.

The plurality of emitter trenches may be disposed at an interval of 3 μmor less from each other.

Also, the emitter trench is preferably formed at the same depth as thatof the gate trench. In this case, the emitter trench is formed by thesame step as that for the gate trench, the manufacturing process can besimplified.

Also, the gate trenches may be disposed one pair each in a transversedirection along the front surface of the semiconductor layer, and thepair of gate trenches may be opposed in the transverse direction via thep-type base region that is common thereto. In this case, one of the pairof gate trenches may be disposed at an interval of 2 μm to 7 μm withrespect to the other.

The n⁺-type emitter region may have an n-type dopant concentration of1×10¹⁹ cm⁻³ to 5×10²⁰ cm⁻³. The p-type base region may have a p-typedopant concentration of 1×10¹⁶ cm⁻³ to 1×10¹⁸ cm⁻³. The n⁻-type driftregion may have an n-type dopant concentration of 1×10¹³ cm⁻³ to 5×10¹⁴cm⁻³. The p⁺-type collector region may have a p-type dopantconcentration of 1×10¹⁵ cm⁻³ to 2×10¹⁹ cm⁻³.

Also, the n⁺-type emitter region preferably selectively has a pulloutportion pulled out in a transverse direction along the front surface ofthe semiconductor layer from a side surface of the gate trench.

Also, the semiconductor device preferably includes a dummy trench formedspaced at a predetermined interval lateral to the gate trench so thatthe n⁻-type emitter region, the p-type base region, and the n⁻-typedrift region are formed between the dummy trench and the gate trench, aburied insulating film being a buried insulating film filled in thedummy trench and having an upper surface on a bottom side of the dummytrench with respect to the front surface of the semiconductor layer, forselectively exposing as a contact region a part of the p-type baseregion at a part from the front surface to the upper surface in a sidesurface of the dummy trench, and a contact electrode filled in a regionover the buried insulating film of the dummy trench, connected to thecontact region on the side surface of the dummy trench.

According to this arrangement, because the side surface of the dummytrench can be effectively used as the contact region, a junction area ofthe contact electrode with respect to the p-type base region can besufficiently secured. Because a plane area of the p-type base region canthereby be sacrificed, the interval between the gate trench and thedummy trench can be miniaturized to form a p-type base region moreminute than the conventional p-type base region. Furthermore, becausethe dummy trench can be formed using the same mask as that for the gatetrench, misalignment with respect to the gate trench does not occur.Moreover, alignment of the contact electrode, for which alignment withan area including a plane area of the dummy trench suffices, can thus beeasily attained.

Also, as a result of miniaturization of the trench structure, atrade-off relationship between the short-circuit capacity and ON-voltageof the device can be improved, so that a charge enhancement effect canbe increased. V_(CE)(sat) in a low-current range can hence be improved.

The semiconductor device may further include a first buried electrodefilled via an insulating film in a region under the buried insulatingfilm of the dummy trench.

Also, the semiconductor device may have a trench unit including a pairof the dummy trenches and a gate trench sandwiched between the pair ofdummy trenches.

Also, the dummy trench preferably serves also as the emitter trench as aresult of the first buried electrode being electrically connected withthe n⁺-type emitter region.

Also, the semiconductor device may have a trench unit including a pairof the gate trenches and a dummy trench sandwiched between the pair ofgate trenches. In this case, the first buried electrode is preferablyelectrically connected with the gate electrode.

Also, the buried insulating film preferably has a thickness of 0.5 μm ormore.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a schematic plan view of a semiconductor device 1 according toa first embodiment of the present invention. FIG. 2 is a sectional viewfrom a section II-II of FIG. 1. FIG. 3 is a sectional view from asection III-III of FIG. 1. FIGS. 4( a) and (b) are views for explainingan internal structure of the semiconductor device of FIG. 1, whereinFIG. 4( a) shows a perspective view, and FIG. 4( b) shows a plan view.

The semiconductor device 1 is a device including IGBTs, and includes asemiconductor substrate 2 as an example of a semiconductor layer of thepresent invention. The semiconductor layer 2 may be, for example, ann⁻-type silicon substrate having a thickness of 50 μm to 200 μm.

The semiconductor substrate 2 has a structure in which a p⁺-typecollector region 4, an n-type buffer region 5, and an n⁻-type driftregion 6 are stacked in order from the side of its back surface 3. Thep⁺-type collector region 4 is exposed over the entire back surface 3 ofthe semiconductor substrate 2, and the n⁻-type drift region 6 isselectively exposed on a part of a front surface 7 of the semiconductorsubstrate 2.

As a p-type dopant of the p⁺-type collector region 4, for example, B(boron), Al (aluminum), and others can be used (the same applies to thefollowing). On the other hand, as an n-type dopant of the n-type bufferregion 5 and the n⁻-type drift region 6, for example, N (nitrogen), P(phosphorus), As (arsenic), and others can be used (the same applies tothe following).

Also, the dopant concentration of the p⁺-type collector region 4 is, forexample, 1×10¹⁵ cm⁻³ to 2×10¹⁹ cm⁻³. On the other hand, the dopantconcentration of the n-type buffer region 5 is, for example, 1×10¹⁵ cm⁻³to 5×10¹⁷ cm⁻³, and the dopant concentration of the n⁻-type drift region6 is 1×10¹³ cm^(−3 to) 5−10¹⁴ cm⁻³.

On the front surface 7 of the semiconductor substrate 2, an activeregion 8 and a non-active region 9 are set adjacent to each other.

On the side of the front surface 7 of the semiconductor substrate 2, aplurality of gate trenches 10 extending across the active region 8 andthe non-active region 9 are formed. In the present embodiment, theplurality of gate trenches 10 are formed in a form of stripes that runacross a boundary between the active region 8 and the non-active region9, and disposed as trench units 11 of one pair each in the transversedirection along the front surface 7 of the semiconductor substrate 2.The pitch P₁ of mutually adjacent trench units 11 is, for example, 4 μmto 20 μm. Also, in a pair of gate trenches 10, the pitch P₂ of one gatetrench 10 and the other gate trench 10 (distance of center points of thegate trenches 10) is, for example, 2 μm to 7 μm, and the interval L₁(distance between side surfaces of the gate trenches 10) is, forexample, 1 μm to 6 μm.

Between a pair of gate trenches 10 in the active region 8, a p-type baseregion 12 is formed, and further, an n⁺-type emitter region 13 is formedin a front surface portion of the p-type base region 12. The p-type baseregion 12 is shared by one gate trench 10 and the other gate trench 10.On the other hand, n³³ -type emitter regions 13 are formed one eachalong side surfaces of one and the other gate trenches 10, and exposedon the front surface 7 of the semiconductor substrate 2. Also, in thefront surface portion of the p-type base region 12, a p⁺-type basecontact region 25 is formed so as to be sandwiched by the pair ofn⁺-type emitter regions 13. The dopant concentration of the p⁺-type basecontact region 25 is, for example, 5×10¹⁸ cm⁻³ to 1×10²⁰ cm⁻³.

The n⁺-type emitter region 13, as shown in FIGS. 4( a) and (b),selectively has a pullout portion 26 pulled out in the transversedirection along the front surface 7 of the semiconductor substrate 2from the side surface of the gate trench 10. The pullout portion 26 is,for example, disposed spaced at fixed intervals along the longitudinaldirection of the gate trench 10. When a pair of n³⁰ -type emitterregions 13 are provided as in the present embodiment, the pulloutportions 26 of the respective n⁺-type emitter regions 13 may be, asshown in FIG. 4( b), disposed so that one and the other end portions areopposed to each other, or end portions of one pullout portion 26 and endportions of the other pullout portion 26 may be disposed alternatelyalong the longitudinal direction of the gate trench 10 (not shown). Inthe former case of an opposing arrangement, a part sandwiched by thepullout portions 26 in the p⁺-type base contact region 25 serves as aconstricted portion 27 selectively having a narrower width than that ofthe remaining part.

Also, in the present embodiment, an interface between the p-type baseregion 12 and the n⁻-type drift region 6 is set in a bottom portion ofthe gate trenches 10, so that the p-type base region 12 is formed bydiffusion up to a relatively deep position of the semiconductorsubstrate 2.

Also, the dopant concentration of the p-type base region 12 is, forexample, 1×10¹⁶ cm⁻³ to 1×10¹⁸ cm⁻³, the dopant concentration of then⁺-type emitter region 13 is 1×10¹⁹ cm⁻³ to 5×10²⁰ cm⁻³.

Also, between a pair of gate trenches 10 on the side of the frontsurface 7 of the semiconductor substrate 2, a plurality of (in FIG. 1 toFIG. 3, three) emitter trenches 14 extending across the active region 8and the non-active region 9 are formed. In the present embodiment, theplurality of emitter trenches 14 are formed in a form of stripes thatrun across a boundary between the active region 8 and the non-activeregion 9 (parallel to the gate trenches 10), and disposed spaced atmutually equal intervals in the transverse direction along the frontsurface 7 of the semiconductor substrate 2. The interval L₂ of mutuallyadjacent emitter trenches 14 (distance between side surfaces of theemitter trenches 14) is, for example, 3 μm or less, and preferably, 0.8μm to 3 μm. Also, the plurality of emitter trenches 14 are formed at thesame depth as that of the gate trenches 10. Because the emitter trenches14 and the gate trenches 10 can thereby be formed by the same step, themanufacturing process can be simplified.

Out of the plurality of emitter trenches 14, a trench that is adjacentto the gate trench 10 (trench that is opposed to the gate trench 10 viano trench therewith) is disposed at an interval L₃ (distance between theside surface of the emitter trench 14 and the side surface of the gatetrench 10) of 2 μm or less via the n⁻-type drift region 6 with the gatetrench 10. That is, between said emitter trench 14 and the gate trench10, the n⁻-type drift region 6 is interposed across the entire area inthe depth direction.

Also, in each section between the plurality of emitter trenches 14 inthe active region 8, a p-type floating region 15 is formed. The p-typefloating region 15 is a semiconductor region where a floating state iselectrically maintained, and is separated from the gate trench 10 by theemitter trench 14 that is adjacent to the gate trench 10. The p-typefloating region 15 is, in the present embodiment, formed at the samedepth as that of the p-type base region 12. That is, an interfacebetween the p-type floating region 15 and the n⁻-type drift region 6 isset in a bottom portion of the emitter trenches 14, so that the p-typefloating region 15 is formed by diffusion up to a relatively deepposition of the semiconductor substrate 2. Because the p-type baseregions 12 and the p-type floating regions 15 can thereby be formed bythe same step, the manufacturing process can be simplified.

Also, the dopant concentration of the p-type floating region 15 is, forexample, 5×10¹⁵ cm⁻³ to 1×10¹⁸ cm⁻³.

On the other hand, in the non-active region 9, for either a regionbetween a pair of gate trenches 10 or a region in each section betweenthe plurality of emitter trenches 14, the n⁻-type drift region 6 extendsacross its entire area.

In the gate trenches 10 and the emitter trenches 14, gate electrodes 17and buried electrodes 18 are filled, respectively, via an insulatingfilm 16 (for example, silicon oxide (SiO₂)). The gate electrodes 17 andthe buried electrodes 18 are made of, for example, a conductive materialsuch as polysilicon. The insulating film 16 is integrally formed alonginner surfaces of the gate trenches 10, the front surface 7 of thesemiconductor substrate 2, and inner surfaces of the emitter trenches14. The part of the insulating film 16 in the gate trench 10 serves as agate insulating film 19. Also, a plurality of buried electrodes 18 ofthe emitter trenches 14 are, in the non-active region 9, connectedcollectively by a contact portion 20. The contact portion 20 is disposedextending across the plurality of buried electrodes 18 in a direction torun across the plurality of emitter trenches 14.

On the front surface 7 of the semiconductor substrate 2, an interlayerfilm 21 made of, for example, an insulating material such as boronphosphorus silicate glass (BPSG) or silicon oxide (SiO₂) is stacked. Inthe interlayer film 21, a contact hole 22 is formed to selectivelyexpose the n⁺-type emitter region 13 and the p⁺-type base contact region25 in the active region 8. The n⁺-type emitter region 13 is selectivelyexposed at the pullout portion 26 from the contact hole 22. Also, in theinterlayer film 21, a contact hole 23 is formed to selectively exposethe contact portion 20 in the non-active region 9.

On the interlayer film 21, an emitter electrode 24 is stacked. Theemitter electrode 24 is connected to the p⁺-type base contact region 25and the n⁺-type emitter region 13 and the contact portion 20 via thecontact holes 22 and 23, respectively. The buried electrodes 18 in theemitter trenches 14 are to be connected to the emitter electrode 24 viathe contact portion 20.

According to the semiconductor device 1, the gate trench 10 filled withthe gate electrode 17 (hereinafter, referred to as a “gate junctiontrench”) is separated from the p-type floating region 15 by the emittertrench 14 filled with the buried electrode 18 (hereinafter, referred toas an “emitter junction trench”). The p-type floating region 15 and thegate junction trench can thereby be prevented from joining. A straycapacitance between the gate junction trench and the p-type floatingregion 15 can therefore be eliminated.

On the other hand, the n⁻-type drift region 6 which the gate junctiontrench joins across the entire area in the depth direction is to begrounded together with the p⁺-type collector region 4. Therefore, atswitching operation, a capacitance change between the gate junctiontrench and the n⁻-type drift region 6 is stabilized, so that noise doesnot easily occur. As a result thereof, generation of noise and switchingloss at switching operation can be reduced.

Also, because the interval L₃ between the emitter junction trench andthe gate junction trench is 2 μm or less, withstand voltage can also besatisfactorily maintained.

Also, in this semiconductor device 1, disposing the contact portion 20in the non-active region 9 allows interposing the relatively thickinterlayer 21 between the emitter electrode 24 and the semiconductorsubstrate 2 in the active region 8. Therefore, insulation breakdown inthe active region 8 can be prevented.

FIG. 5 is a schematic sectional view of a semiconductor device 41according to a second embodiment of the present invention. In FIG. 5,parts corresponding to the respective portions shown in FIG. 2 and FIG.3 described above will be denoted by the same reference signs.

In the foregoing first embodiment, an interface between the p-type baseregion 12 and the n⁻-type drift region 6 is set in a bottom portion ofthe gate trenches 10, so that the p-type base region 12 is formed bydiffusion up to a relatively deep position of the semiconductorsubstrate 2. In contrast, in the semiconductor device 41 of the secondembodiment, an interface between a p-type base region 42 and the n⁻-typedrift region 6 is set in a central portion or upper portion of the gatetrenches 10, so that the p-type base region 42 is formed by diffusion ata relatively shallow position of the semiconductor substrate 2.

Also, the semiconductor device 41 includes a p-type floating region 43formed deeper than the p-type base region 42 in each section between theplurality of emitter trenches 14. The p-type floating region 43 has abottom portion 44 that bulges to the side of the back surface 3 of thesemiconductor substrate 2 with respect to a bottom portion of theemitter trenches 14 and an overlap portion 45 that goes around to thelower side of the emitter trench 14 adjacent to the gate trench 10. Theoverlap portion 45 has an end portion 46 positioned on a side closer tothe gate trench 10 with respect to the center in the width direction ofsaid emitter trench 14. The end portion 46 is preferably not projectingto the side of the gate trench 10 with respect to the emitter trench 14.

Next, a manufacturing method of the semiconductor device 41 will beexplained. FIG. 6A to FIG. 6G are views for explaining the manufacturingprocess of the semiconductor device 41 of FIG. 5 in the order of steps.

For manufacturing the semiconductor device 41, as shown in FIG. 6A, amask 47 is formed on the front surface 7 of the n⁻-type semiconductorsubstrate 2 (n⁻-type drift region 6). In the mask 47, there is formed anopening to selectively expose a region that needs to be formed into thep-type floating region 43 in the front surface 7. Then, via the mask 47,a p-type dopant is ion-implanted into the front surface 7 of thesemiconductor substrate 2. An ion-implanted region 48 is thereby formed.

Next, as shown in FIG. 6B, by the semiconductor substrate 2 beingselectively etched, the gate trenches 10 and the emitter trenches 14 aresimultaneously formed.

Next, as shown in FIG. 6C, by the semiconductor substrate 2 beingthermally oxidized, a sacrificial oxide film 49 is formed on the entirearea of the front surface including the inner surfaces of the gatetrenches 10 and the emitter trenches 14. Then, by annealing thesemiconductor substrate 2 covered with the sacrificial oxide film 49,the p-type dopant in the ion-implanted region 48 is diffused (drivenin). The annealing treatment is performed on a condition that the p-typedopant goes around to the lower side of the emitter trench 14. Thep-type floating region 43 is thereby formed. In this case, because thesemiconductor substrate 2 is covered with the sacrificial oxide film 49,ion seeping from the front surface of the substrate can be prevented, sothat the p-type dopant can be efficiently diffused.

Next, as shown in FIG. 6D, the sacrificial oxide film 49 is stripped.

Next, as shown in FIG. 6E, by the semiconductor substrate 2 beingthermally oxidized, the insulating film 16 (gate insulating film 19) isformed on the entire area of the front surface including the innersurfaces of the gate trenches 10 and the emitter trenches 14.

Next, as shown in FIG. 6F, an electrode material such as polysilicon isfilled in the gate trenches 10 and the emitter trenches 14. The gateelectrodes 17 and the buried electrodes 18 are simultaneously formed.

Next, as shown in FIG. 6G, by n-type and p-type dopants beingselectively ion-implanted and diffused into the front surface 7 of thesemiconductor substrate 2, the p-type base regions 42, the n⁺-typeemitter regions 13, and the p⁺-type base contact regions 25 are therebyformed in order.

Thereafter, by n-type and p-type dopants being selectively ion-implantedand diffused into the back surface 3 of the semiconductor substrate 2after the interlayer film 21 and the emitter electrode 24 and the likebeing formed on the side of the front surface 7 of the semiconductorsubstrate 2, the n-type buffer region 5 and the p⁺-type collector region4 are formed in order.

Through the steps as above, the semiconductor device 41 shown in FIG. 5is obtained. However, FIG. 6A to FIG. 6G merely represent a part of themanufacturing process of the semiconductor device 41, and saidmanufacturing process may include steps not shown by FIG. 6A to FIG. 6G.

According to this semiconductor device 41, because the p-type floatingregion 43 (overlap portion 45) is formed up to a bottom portion of theemitter junction trench, a collector-emitter voltage to be loaded on theemitter junction trench at switching-off operation can be relieved.Therefore, a device breakdown can be prevented against a steep voltagechange (dv/dt).

Also, because withstand voltage can be increased by the p-type floatingregion 43 that is deeper than the p-type base region 42, while thep-type base region 42 may be shallow, the channel length (length in thedepth direction of the gate trench 10) can also be reduced to suppress arise in ON-voltage by appropriately designing the depth of the p-typebase region 42.

Of course, the same effects as those of the semiconductor device 1 ofthe first embodiment can also be achieved.

FIG. 7 is a schematic sectional view of a semiconductor device 51according to a third embodiment of the present invention. FIG. 8 is aperspective view for explaining an internal structure of thesemiconductor device 51 of FIG. 7. In FIG. 7 and FIG. 8, partscorresponding to the respective portions shown in FIG. 2 to FIG. 5described above will be denoted by the same reference signs.

In the foregoing first and second embodiments, the emitter electrode 24is connected to the p⁺-type base contact regions 25 and the n⁺-typeemitter regions 13 on the front surface 7 of the semiconductor substrate2. In contrast, the semiconductor device 51 of the third embodimentfurther includes a contact trench 52 formed penetrating through then⁺-type emitter regions 13 from the front surface 7 of the semiconductorsubstrate 2 in the p-type base region 42 and a p⁺-type base contactregion 53 formed on a bottom surface of said contact trench region 52.The contact trench 52 is formed with a fixed width along thelongitudinal direction of the gate trench 10. The n⁺-type emitter region13 is exposed on a side surface of the contact trench 52, and thep⁺-type base contact region 53 is exposed on the bottom surface of thecontact trench 52. The dopant concentration of the p⁺-type base contactregion 53 is, for example, 5×10¹⁸ cm³¹ ³ to 1×10²⁰ cm⁻³.

Moreover, the emitter electrode 24 enters the contact trench 52, and isconnected to the n⁺-type emitter region 13 on the side surface of thecontact trench 52. Also, on the bottom surface of the contact trench 52,the emitter electrode 24 is connected to the p-type base region 42 viathe p⁺-type base contact region 53.

According to this semiconductor device 51, because the side surface ofthe contact trench 52 can be effectively used as a region for contactwith the n⁺-type emitter region 13, a junction area of the emitterelectrode 24 with respect to the n⁺-type emitter region 13 can besufficiently secured. Because a plane area of the n⁺-type emitter region13 can thereby be sacrificed, the interval L₁ between one and the othergate trenches 10 of a pair of gate trenches 10 can be miniaturized toform a p-type base region 42 more minute than the conventional p-typebase region. As a result of miniaturization of the gate trench 10, atrade-off relationship between the short-circuit capacity and ON-voltageof the device can be improved, so that a charge enhancement effect canbe increased. V_(CE)(sat) in a low-current range can hence be improved.

Of course, the same effects as those of the semiconductor devices 1 and41 of the first and second embodiments can also be achieved.

FIG. 9 is a schematic sectional view of a semiconductor device 61according to a fourth embodiment of the present invention. In FIG. 9,parts corresponding to the respective portions shown in FIG. 2 and FIG.3 described above will be denoted by the same reference signs.

In the foregoing first embodiment, a plurality of emitter trenches 14are formed between a pair of gate trenches 10, and the p-type floatingregion 15 is formed in each section between the plurality of emittertrenches 14. In contrast, in the semiconductor device 61 of the fourthembodiment, a single emitter trench 62 is formed between a pair of gatetrenches 10, and the p-type floating region 15 is omitted.

Also by this semiconductor device 61, the same effects as those of thesemiconductor device 1 of the first embodiment can be achieved.

FIG. 10 is a schematic sectional view of a semiconductor device 71according to a fifth embodiment of the present invention. In FIG. 10,parts corresponding to the respective portions shown in FIG. 2 and FIG.3 described above will be denoted by the same reference signs.

In the foregoing first embodiment, the contact portion 20 thatcollectively connects the plurality of buried electrodes 18 is disposedin the non-active region 9. In contrast, the semiconductor device 71 ofthe fifth embodiment includes, in the active region 8, a contact portion72 that is disposed extending across the plurality of buried electrodes18 in a direction to run across the plurality of emitter trenches 14.Also, in the interlayer film 21, a contact hole 73 is formed toselectively expose said contact portion 72. Thus, the plurality ofburied electrodes 18 of the emitter trenches 14 are, in the activeregion 8, connected collectively by the contact portion 72.

Also by this semiconductor device 71, the same effects as those of thesemiconductor device 1 of the first embodiment can be achieved.

FIG. 11 is a schematic sectional view of a semiconductor device 101according to a sixth embodiment of the present invention. FIG. 12 is anenlarged view of a part enclosed by a broken line of FIG. 11.

The semiconductor device 101 is a device including IGBTs, and includes asemiconductor substrate 102 as an example of a semiconductor layer ofthe present invention. The semiconductor substrate 102 may be, forexample, an n⁻-type silicon substrate having a thickness of 50 μm to 200μm.

The semiconductor substrate 102 has a structure in which a p⁺-typecollector region 104, an n-type buffer region 105, and an n⁻-type driftregion 106 are stacked in order from the side of its back surface 103.The p⁺-type collector region 104 is exposed over the entire back surface103 of the semiconductor substrate 102, and the n⁻-type drift region 106is selectively exposed on a part of a front surface 107 of thesemiconductor substrate 102.

As a p-type dopant of the p⁺-type collector region 104, for example, B(boron), Al (aluminum), and others can be used (the same applies to thefollowing). On the other hand, as an n-type dopant of the n-type bufferregion 105 and the n⁻-type drift region 106, for example, N (nitrogen),P (phosphorus), As (arsenic), and others can be used (the same appliesto the following).

Also, the dopant concentration of the p⁺-type collector region 104 is,for example, 1×10¹⁵ cm⁻³ to 2×10¹⁹ cm⁻³. On the other hand, the dopantconcentration of the n-type buffer region 105 is, for example, 1×10¹⁵cm⁻³ to 5×10¹⁷ cm⁻³, and the dopant concentration of the n⁻-type driftregion 106 is 1×10¹³ cm⁻³ to 5×10¹⁴ cm⁻³.

On the side of the front surface 107 of the semiconductor substrate 102,a plurality of gate trenches 108 and a plurality of dummy trenches 109are formed adjacent to each other. In the present embodiment, a trenchunit 110 including a pair of dummy trenches 109 and a gate trench 108sandwiched between the pair of dummy trenches 109 is disposed in pluralnumbers spaced at intervals in the transverse direction along the frontsurface 107 of the semiconductor substrate 102. The gate trenches 108and the dummy trenches 109 are thereby formed in a stripe form as awhole.

The pitch P₁ of mutually adjacent trench units 110 is, for example, 2 μmto 7 μm. Also, in each trench unit 110, the intervals L₁ between thegate trench 108 and the dummy trenches 109 on both sides thereof(distances between side surfaces of the gate trench 108 and sidesurfaces of the dummy trenches 109) are preferably respectively 2 μm orless.

In each trench unit 100, on both sides of the gate trench 108 (regionsbetween the same and the respective dummy trenches 109), a p-type baseregion 111 is formed, and further, an n⁺-type emitter region 112 and ap⁺-type base contact region 113 are formed in a front surface portion ofthe p-type base region 111 (refer to FIG. 12). In the presentembodiment, an interface between the p-type base region 111 and then⁻-type drift region 106 is set in a central portion or upper portion ofthe gate trench 108, and the p-type base region 111 is formed bydiffusion at a relatively shallow position of the semiconductorsubstrate 102.

The n⁺-type emitter region 112 and the p⁺-type base contact region 113are disposed adjacent to each other in the region between the gatetrench 108 and the dummy trench 109. Specifically, n⁺-type emitterregions 112 are formed one each along both side surfaces 114 of the gatetrench 108, and p⁺-type base contact regions 113 are formed one eachalong side surfaces 115 of the respective dummy trenches 109. Then⁺-type emitter regions 112 are thereby exposed on the front surface 107of the semiconductor substrate 102 and the side surfaces 114 of the gatetrenches 108. On the other hand, the p⁺-type base contact regions 113are exposed on the front surface 107 of the semiconductor substrate 102and the side surfaces 115 of the dummy trenches 109.

Also, the dopant concentration of the p-type base region 111 is, forexample, 1×10¹⁶ cm⁻³ to 1×10¹⁸ cm⁻³. The dopant concentration of then⁺-type emitter region 112 is 1×10¹⁹ cm⁻³ to 5×10²⁰ cm⁻³. The dopantconcentration of the p⁺-type base contact region 113 is, for example,5×10¹⁸ cm⁻³ to 1×10²⁰ cm⁻³.

Also, between trench units 110 adjacent on the side of the front surface107 of the semiconductor substrate 102, a plurality of (in FIG. 11,three) emitter trenches 116 are formed. In the present embodiment, theplurality of emitter trenches 116 are formed in, for example, a stripeform (parallel to the gate trenches 108 and the dummy trenches 109), anddisposed spaced at mutually equal intervals in the transverse directionalong the front surface 107 of the semiconductor substrate 102. Theinterval L₂ of mutually adjacent emitter trenches 116 (distance betweenside surfaces of the emitter trenches 116) is, for example, 3 μm orless, and preferably, 0.8 μm to 3 μm. Also, the plurality of emittertrenches 116 are formed at the same depth as that of the gate trenches108 and the dummy trenches 109. Because the emitter trenches 116 canthereby be formed by the same step as that for the gate trenches 108 andthe dummy trenches 109, the manufacturing process can be simplified.

Out of the plurality of emitter trenches 116, a trench that is adjacentto the dummy trench 109 (trench that is opposed to the dummy trench 109via no trench therewith) is disposed at an interval L₃ (distance betweenthe side surface of the emitter trench 116 and the side surface of thedummy trench 109) of 0.5 μm to 20 μm with the dummy trench 109.

Also, in the semiconductor substrate 102, a p-type floating region 117is formed. The p-type floating region 117 spreads over a regionsandwiched by the dummy trenches 109 of mutually adjacent trench units110, opposed via the emitter trenches 116. The p-type floating region117 is a semiconductor region where a floating state is electricallymaintained, and is separated from the gate trench 108 by the dummytrench 109 that is adjacent to the gate trench 108. The p-type floatingregion 117 is, in the present embodiment, formed deeper than the p-typebase region 111.

The p-type floating region 117 has a bottom portion 118 that bulges tothe side of the back surface 103 of the semiconductor substrate 102 withrespect to a bottom portion of the emitter trenches 116 and an overlapportion 119 that goes around to the lower side of the dummy trench 109.The overlap portion 119 has an end portion 120 positioned on a sidecloser to the gate trench 108 with respect to the center in the widthdirection of said dummy trench 109. The end portion 120 is preferablynot projecting to the side of the gate trench 108 with respect to theemitter trench 116.

Also, the dopant concentration of the p-type floating region 117 is, forexample, 5×10¹⁵ cm⁻³ to 1×10¹⁸ cm⁻³.

In the gate trenches 108, the dummy trenches 109, and the emittertrenches 116, gate electrodes 122, first buried electrodes 123, andsecond buried electrodes 124 are filled, respectively, via an insulatingfilm 121 (for example, silicon oxide (SiO₂)). The gate electrodes 122,the first buried electrodes 123, and the second buried electrodes 124are made of, for example, a conductive material such as polysilicon. Theinsulating film 121 is integrally formed along inner surfaces of thegate trenches 108, inner surfaces of the dummy trenches 109, the frontsurface 107 of the semiconductor substrate 102, and inner surfaces ofthe emitter trenches 116. The part of the insulating film 121 in thegate trench 108 serves as a gate insulating film 125. Also, the firstburied electrodes 123 and the second buried electrodes 124 areelectrically connected to an emitter electrode 132 to be describedlater.

Also, in the present embodiment, the gate electrode 122 and the secondburied electrode 124 fill back their respective trenches 108 and 116 upto the opening ends, whereas the first buried electrode 123 fills backthe dummy trench 109 halfway in the depth direction thereof. In thedummy trench 109, a space without an electrode is thereby formed in aregion over the first buried electrode 123. Moreover, a buriedinsulating film 126 is filled in the dummy trench 109 so as to fill backthe space up to the opening end.

The buried insulating film 126 is made of, for example, an insulatingmaterial such as boron phosphorus silicate glass (BPSG) or silicon oxide(SiO₂), and has a thickness of 0.5 μm or more. In the buried insulatingfilm 126 and the insulating film 121 thereunder, a removal portion 127is selectively formed to expose the p⁺-type base contact region 113 onthe side surface 115 of the dummy trench 109. That is, the buriedinsulating film 126 selectively has an upper surface 128 that is at aposition lower than that of the front surface 107 of the semiconductorsubstrate 102 so as to be continuous from the side surface 115 of thedummy trench 109, and the p⁺-type base contact region 113 is exposed ina region of the side surface 115 of the dummy trench 109 between theupper surface 128 and the front surface 107.

On the front surface 107 of the semiconductor substrate 102, aninterlayer film 129 made of, for example, an insulating material such asboron phosphorus silicate glass (BPSG) or silicon oxide (SiO₂) isstacked. The interlayer film 129 is formed integrally with the buriedinsulating film 126. In the interlayer film 129, a contact hole 130 isformed extending across the front surface 107 of the semiconductorsubstrate 102 and the opening end of the dummy trench 109. The contacthole 130 exposes the n⁺-type emitter region 112 and the p⁺-type basecontact region 113 at the front surface 107 of the semiconductorsubstrate 102, and exposes the p⁺-type base contact region 113 at theside surface 115 (removal portion 127) of the dummy trench 109. That is,the p⁺-type base contact region 113 is exposed in a corner portion 131of the dummy trench 109 defined by intersection of the front surface 107and the side surface 115. In addition, the n⁺-type emitter region 112may selectively have a pullout portion pulled out in the transversedirection along the front surface 107 of the semiconductor substrate 102from the side surface 114 of the gate trench 108, and only the pulloutportion may be selectively exposed from the contact hole 130.

On the interlayer film 129, an emitter electrode 132 as an example of acontact electrode of the present invention is stacked. The emitterelectrode 132 enters the contact hole 130, and is connected to then⁺-type emitter region 112 on the front surface 107 of the semiconductorsubstrate 102, and is connected to the p⁺-type base contact region 113in the corner portion 131 of the dummy trench 109.

Next, a manufacturing method of the semiconductor device 101 will beexplained. FIG. 13A to FIG. 13K are views for explaining themanufacturing process of the semiconductor device 101 of FIG. 11 and theFIG. 12 in the order of steps. In addition, FIG. 13A to FIG. 13F showsections corresponding to FIG. 11, and FIG. 13G to FIG. 13K showsections corresponding to FIG. 12.

For manufacturing the semiconductor device 101, as shown in FIG. 13A, amask 160 is formed on the front surface 107 of the n⁻-type semiconductorsubstrate 102 (n⁻-type drift region 106). In the mask 160, there isformed an opening to selectively expose a region that needs to be formedinto the p-type floating region 117 in the front surface 107. Then, viathe mask 160, a p-type dopant is ion-implanted into the front surface107 of the semiconductor substrate 102. An ion-implanted region 161 isthereby formed.

Next, as shown in FIG. 13B, by the semiconductor substrate 102 beingselectively etched, the gate trenches 108, the dummy trenches 109, andthe emitter trenches 116 are simultaneously formed.

Next, as shown in FIG. 13C, by the semiconductor substrate 102 beingthermally oxidized, a sacrificial oxide film 162 is formed on the entirearea of the front surface including the inner surfaces of the gatetrenches 108, the dummy trenches 109, and the emitter trenches 116.Then, by annealing the semiconductor substrate 102 covered with thesacrificial oxide film 162, the p-type dopant in the ion-implantedregion 161 is diffused (driven in). The annealing treatment is performedon a condition that the p-type dopant goes around to the lower side ofthe dummy trench 109. The p-type floating region 117 is thereby formed.In this case, because the semiconductor substrate 102 is covered withthe sacrificial oxide film 162, ion seeping from the front surface ofthe substrate can be prevented, so that the p-type dopant can beefficiently diffused.

Next, as shown in FIG. 13D, the sacrificial oxide film 162 is stripped.

Next, as shown in FIG. 13E, by the semiconductor substrate 102 beingthermally oxidized, the insulating film 121 (gate insulating film 125)is formed on the entire area of the front surface including the innersurfaces of the gate trenches 108, the dummy trenches 109, and theemitter trenches 116.

Next, as shown in FIG. 13F, an electrode material such as polysilicon isfilled in the gate trenches 108, the dummy trenches 109, and the emittertrenches 116. The gate electrodes 122, the first buried electrodes 123,and the second buried electrodes 124 are thereby simultaneously formed.

Next, as shown in FIG. 13G, by n-type and p-type dopants beingselectively ion-implanted and diffused into the front surface 107 of thesemiconductor substrate 102, the p-type base regions 111 and the n⁺-typeemitter regions 112 are formed in order.

Next, as shown in FIG. 13H, by etching the first buried electrodes 123from upper surfaces, the filled states of the gate electrodes 122 andthe second buried electrodes 124 are kept maintained, while only thefirst buried electrodes 123 are selectively dug down.

Next, as shown in FIG. 13I, by depositing an insulating material such asboron phosphorus silicate glass (BPSG) or silicon oxide (SiO₂) on thefront surface 107 of the semiconductor substrate 102, the spaces overthe first buried electrodes 123 are filled back with said insulatingmaterial, and the front surface 107 is covered with said insulatingmaterial. The buried insulating film 126 and the interlayer film 129 arethereby simultaneously formed.

Next, as shown in FIG. 13J, by selectively etching the interlayer film129 and the buried insulating film 126, the contact holes 130 and theremoval portions 127 are simultaneously formed.

Next, as shown in FIG. 13K, a p-type dopant is selectively ion-implantedand diffused into the front surface 107 of the semiconductor substrate102 exposed in the contact holes 130. The p⁺-type base contact regions113 are thereby formed.

Thereafter, by n-type and p-type dopants being selectively ion-implantedand diffused into the back surface 103 of the semiconductor substrate102 after the emitter electrode 132 and the like being formed on theside of the front surface 107 of the semiconductor substrate 102, then-type buffer region 105 and the p⁺-type collector region 104 are formedin order.

Through the steps as above, the semiconductor device 101 shown in FIG.11 and FIG. 12 is obtained. However, FIG. 13A to FIG. 13K merelyrepresent a part of the manufacturing process of the semiconductordevice 101, and said manufacturing process may include steps not shownby FIG. 13A to FIG. 13K.

According to this semiconductor device 101, because the side surface 115of the dummy trench 109 can be effectively used as the p⁺-type basecontact region 113, a junction area of the emitter electrode 132 withrespect to the p-type base region 111 can be sufficiently secured byboth surfaces of the front surface 107 of the semiconductor substrate102 and the side surface 115 of the dummy trench 109. Because a planearea of the p-type base region 111 can thereby be sacrificed, theinterval L₁ between the gate trench 108 and the dummy trench 109 can beminiaturized to form a p-type base region 111 more minute than theconventional p-type base region. Furthermore, because the dummy trenches109 can be formed using the same mask as that for the gate trenches 108,misalignment with respect to the gate trenches 108 does not occur.Moreover, alignment of the emitter electrode 132, for which alignmentwith an area including a plane area of the dummy trenches 109 suffices,can thus be easily attained.

Specifically, first, by etching the semiconductor substrate 102 usingthe same mask, the gate trenches 108, the dummy trenches 109, and theemitter trenches 116 are simultaneously formed (FIG. 13B). Next, byfilling polysilicon in the trenches 108, 109, and 116, the gateelectrodes 122, the first buried electrodes 123, and the second buriedelectrodes 124 are formed (FIG. 13F). Next, a mask to selectively exposethe dummy trenches 109 is formed on the semiconductor substrate 102, andvia the mask, an upper portion of the polysilicon in the dummy trenches109 is selectively removed by etching. Spaces are thereby formed inregions over the first buried electrodes 123 of the dummy trenches 109(FIG. 13H). Next, the interlayer film 129 is formed by depositing on thesemiconductor substrate 102 an insulating material such as BPSG by, forexample, a CVD method (FIG. 13I). A part of the insulating materialenters into the dummy trenches 109 as the buried insulating film 126.Next, a mask to form the contact holes 130 is aligned with respect tothe semiconductor substrate 102. In this case, because end portions ofthe contact holes 130 may cover the dummy trenches 109, the alignmentcan be attained in a wide area including the front surface 107 of thesemiconductor substrate 102 and a plane area of the dummy trenches 109.Then, via said mask, the interlayer film 129 and the buried insulatingfilm 126 are continuously etched. The contact holes 130 and the removalportions 127 are thereby simultaneously formed (FIG. 13J). Thereafter,by ion-implanting a p-type dopant using the interlayer film 129 as amask to form the p⁺-type base contact regions 113 in a self-alignedmanner, the p⁺-type base contact regions 113 can be reliably formed inthe corner portions 131 of the dummy trenches 109 (FIG. 13K).Furthermore, because the contact holes 130 can be formed relativelywide, a part of the emitter electrode 132 using aluminum (Al) or thelike can be used as plugs, even without using plugs excellent in fillingability, such as tungsten (W).

As a result of miniaturization of the trench structure as above, atrade-off relationship between the short-circuit capacity and ON-voltageof the device can be improved, so that a charge enhancement effect canbe increased. V_(CE)(sat) in a low-current range can hence be improved.

Also, according to this semiconductor device 101, the gate trench 108filled with the gate electrode 122 (hereinafter, referred to as a “gatejunction trench”) is separated from the p-type floating region 117 bythe dummy trench 109 filled with the first buried electrode 123connected to the n⁺-type emitter region 112 (hereinafter, referred to asan “emitter junction trench”). The p-type floating region 117 and thegate junction trench can thereby be prevented from joining. A straycapacitance between the gate junction trench and the p-type floatingregion 117 can therefore be eliminated.

On the other hand, the n⁻-type drift region 106 which the gate junctiontrench joins across the depth direction is to be grounded together withthe p⁺-type collector region 104. Therefore, at switching operation, acapacitance change between the gate junction trench and the n⁻-typedrift region 106 is stabilized, so that noise does not easily occur. Asa result thereof, generation of noise and switching loss at switchingoperation can be reduced.

Also, because the interval L₁ between the emitter junction trench andthe gate junction trench is 2 μm or less, withstand voltage can also besatisfactorily maintained.

Further, according to this semiconductor device 101, because the p-typefloating region 117 (overlap portion 119) is formed up to a bottomportion of the emitter junction trench, a collector-emitter voltage tobe loaded on the emitter junction trench at switching-off operation canbe relieved. Therefore, a device breakdown can be prevented against asteep voltage change (dv/dt).

Also, because withstand voltage can be increased by the p-type floatingregion 117 that is deeper than the p-type base region 111, while thep-type base region 111 may be shallow, the channel length (length in thedepth direction of the gate trench 108) can also be reduced to suppressa rise in ON-voltage by appropriately designing the depth of the p-typebase region 111.

FIG. 14 is a schematic sectional view of a semiconductor device 141according to a seventh embodiment of the present invention. FIG. 15 isan enlarged view of a part enclosed by a broken line of FIG. 14. In FIG.14 and FIG. 15, parts corresponding to the respective portions shown inFIG. 11 and FIG. 12 described above will be denoted by the samereference signs.

In the foregoing sixth embodiment, the trench unit 110 includes a pairof dummy trenches 109 and a gate trench 108 sandwiched between the pairof dummy trenches 109. In contrast, the semiconductor device 141 of theseventh embodiment has a trench unit 144 including a pair of gatetrenches 142 and a dummy trench 143 sandwiched between the pair of gatetrenches 142. In this case, the interval L₃ between the gate trench 142and the emitter trench 116 (distance between the side surface of thegate trench 142 and the side surface of the emitter trench 116) ispreferably 2 μm or less.

In each trench unit 144, on both sides of the dummy trench 143 (regionsbetween the same and the respective gate trenches 142), a p-type baseregion 145 is formed, and further, an n⁺-type emitter region 146 and ap⁺-type base contact region 147 are formed in a front surface portion ofthe p-type base region 145 (refer to FIG. 15). In the presentembodiment, an interface between the p-type base region 145 and then⁻-type drift region 106 is set in a central portion or upper portion ofthe gate trench 142, and the p-type base region 145 is formed bydiffusion at a relatively shallow position of the semiconductorsubstrate 102.

The n⁺-type emitter region 146 and the p⁺-type base contact region 147are disposed adjacent to each other in the region between the gatetrench 142 and the dummy trench 143. Specifically, n⁺-type emitterregions 146 are formed one each along side surfaces 148 of therespective gate trenches 142, and p⁺-type base contact regions 147 areformed one each along both side surfaces 149 of the dummy trench 143.The n⁺type emitter regions 146 are thereby exposed on the front surface107 of the semiconductor substrate 102 and the side surfaces 148 of thegate trenches 142. On the other hand, the p⁺-type base contact regions147 are exposed on the front surface 107 of the semiconductor substrate102 and the side surfaces 149 of the dummy trenches 143.

Also, in the semiconductor substrate 102, a p-type floating region 150is formed. The p-type floating region 150 spreads over each sectionbetween the plurality of emitter trenches 116. The p-type floatingregion 150 is a semiconductor region where a floating state iselectrically maintained, and is separated from the gate trench 142 bythe emitter trench 116 that is adjacent to the gate trench 142. Thep-type floating region 150 is, in the present embodiment, formed deeperthan the p-type base region 145.

The p-type floating region 150 has a bottom portion 151 that bulges tothe side of the back surface 103 of the semiconductor substrate 102 withrespect to a bottom portion of the emitter trenches 116 and an overlapportion 152 that goes around to the lower side of the emitter trench 116adjacent to the gate trench 142. The overlap portion 152 has an endportion 153 positioned on a side closer to the gate trench 142 withrespect to the center in the width direction of said emitter trench 116.The end portion 153 is preferably not projecting to the side of the gatetrench 142 with respect to the emitter trench 116.

Such a p-type floating region 150 can be formed, for example, in thesame manner as the foregoing p-type floating region 117.

In the dummy trench 143, a first buried electrode 154 is filled via aninsulating film 121. The first buried electrode 154 is made of, forexample, a conductive material such as polysilicon, and is electricallyconnected to the gate electrode 122. Also, the first buried electrode154 fills back the dummy trench 143 halfway in the depth directionthereof. In the dummy trench 143, a space without an electrode isthereby formed in a region over the first buried electrode 154.Moreover, a buried insulating film 155 is filled in the dummy trench 143so as to fill back the space up to the opening end.

The buried insulating film 155 is made of, for example, an insulatingmaterial such as boron phosphorus silicate glass (BPSG) or silicon oxide(SiO₂), and has a thickness of 0.5 μm or more. In the buried insulatingfilm 155 and the insulating film 121 thereunder, a removal portion 156is selectively formed to expose the p⁺-type base contact regions 147 onboth side surfaces 149 of the dummy trench 143. That is, the buriedinsulating film 155 selectively has an upper surface 157 that is at aposition lower than that of the front surface 107 of the semiconductorsubstrate 102 so as to be continuous from both side surfaces 149 of thedummy trench 143, and the p⁺-type base contact regions 147 are exposedin a region of both side surfaces 149 of the dummy trench 143 betweenthe upper surface 157 and the front surface 107.

In the interlayer film 129, a contact hole 158 is formed extendingacross the p-type base regions 145 opposed across the dummy trench 143.The contact hole 158 exposes the n⁺-type emitter regions 146 and thep⁺-type base contact regions 147 at the front surface 107 of thesemiconductor substrate 102, and exposes the p⁺-type base contactregions 147 at both side surfaces 149 (removal portion 156) of the dummytrench 143. That is, the p⁺-type base contact regions 147 are exposed inboth corner portions 159 of the dummy trench 143 defined by intersectionof the front surface 107 and the side surfaces 149. In addition, then⁺-type emitter region 146 may selectively have a pullout portion pulledout in the transverse direction along the front surface 107 of thesemiconductor substrate 102 from the side surface 148 of the gate trench142, and only the pullout portion may be selectively exposed from thecontact hole 158.

Moreover, the emitter electrode 132 enters the contact hole 158, and isconnected to the n⁺-type emitter regions 146 on the front surface 107 ofthe semiconductor substrate 102, and is connected to the p⁺-type basecontact regions 147 in both corner portions 159 of the dummy trench 143.

Also by this semiconductor device 141, the same effects as those of thesemiconductor device 101 of the sixth embodiment can be achieved.

The embodiments of the present invention are described above, however,the present invention can also be carried out in other embodiments.

For example, the above-described features grasped from the disclosuresof the respective embodiments described above may be combined with eachother even among different embodiments.

Also, in the foregoing embodiments, only the arrangements of IGBTsincluded in the semiconductor devices 1, 41, 51, 61, 71, 101, and 141are illustrated, however, a semiconductor device of the presentinvention may include elements other than IGBTs (for example, MOSFETs,diodes, and the like) in a region different from a forming region ofIGBTs.

Various other design modifications can be made within the scope of thematters described in the claims.

The embodiments of the present invention are merely specific examplesused to clarify the technical contents of the present invention, and thepresent invention should not be interpreted as being limited to onlythese specific examples, and the spirit and scope of the presentinvention shall be limited only by the accompanying claims.

The present application corresponds to Japanese Patent Application No.2012-182169 filed on Aug. 21, 2012 in the Japan Patent Office, JapanesePatent Application No. 2012-182168 filed on Aug. 21, 2012 in the JapanPatent Office, and Japanese Patent Application No. 2013-167477 filed onAug. 12, 2013 in the Japan Patent Office, and the entire disclosures ofthese applications are incorporated herein by reference.

In addition, from the description of the specification and drawings, thefollowing features can be extracted besides the inventions described inthe claims.

(Section 1) A semiconductor device including a semiconductor layer, agate trench formed in the semiconductor layer, a gate electrode filledvia a gate insulating film in the gate trench, a dummy trench formedspaced at a predetermined interval lateral to the gate trench, ann⁺-type emitter region, a p-type base region, and an n⁻-type driftregion disposed, in a region between the gate trench and the dummytrench, in order in a depth direction of the gate trench from a frontsurface side of the semiconductor layer, a p⁺-type collector regiondisposed on a back surface side of the semiconductor layer with respectto the n⁻-type drift region, a buried insulating film being a buriedinsulating film filled in the dummy trench and having an upper surfaceat a bottom side of the dummy trench with respect to the front surfaceof the semiconductor layer, for selectively exposing as a contact regiona part of the p-type base region at a part from the front surface to theupper surface in a side surface of the dummy trench, and a contactelectrode filled in a region over the buried insulating film of thedummy trench, connected to the contact region on the side surface of thedummy trench.

According to this arrangement, because the side surface of the dummytrench can be effectively used as the contact region, a junction area ofthe contact electrode with respect to the p-type base region can besufficiently secured. Because a plane area of the p-type base region canthereby be sacrificed, the interval between the gate trench and thedummy trench can be miniaturized to form a p-type base region moreminute than the conventional p-type base region. Furthermore, becausethe dummy trench can be formed using the same mask as that for the gatetrench, misalignment with respect to the gate trench does not occur.Moreover, alignment of the contact electrode, for which alignment withan area including a plane area of the dummy trench suffices, can thus beeasily attained.

Also, as a result of miniaturization of the trench structure, atrade-off relationship between the short-circuit capacity and ON-voltageof the device can be improved, so that a charge enhancement effect canbe increased. V_(CE)(sat) in a low-current range can hence be improved.

(Section 2) The semiconductor device according to section 1, wherein thesemiconductor device further includes a first buried electrode filledvia an insulating film in a region under the buried insulating film ofthe dummy trench.

(Section 3) The semiconductor device according to section 2, wherein thesemiconductor device has a trench unit including a pair of the dummytrenches and a gate trench sandwiched between the pair of dummytrenches.

(Section 4) The semiconductor device according to section 3, wherein thefirst buried electrode is electrically connected with the n⁺-typeemitter region.

(Section 5) The semiconductor device according to section 4, wherein thetrench unit is formed in plural numbers in a transverse direction alongthe front surface of the semiconductor layer, and the semiconductordevice further includes a plurality of emitter trenches formed betweenthe trench units adjacent to each other, a second buried electrodefilled via an insulating film in the emitter trench, electricallyconnected with the n⁺-type emitter region, and a p-type floating regionformed between the dummy trench of the trench unit and the dummy trenchof the trench unit next thereto.

(Section 6) The semiconductor device according to section 5, wherein thep-type floating region is formed deeper than the p-type base region, andincludes an overlap portion that goes around to a lower side of thedummy trench.

According to this arrangement, because the p-type floating region(overlap portion) is formed up to a bottom portion of the dummy trenchfilled with the first buried electrode connected to the n⁺-type emitterregion (hereinafter, referred to as an “emitter junction trench”), acollector-emitter voltage to be loaded on the emitter junction trench atswitching-off operation can be relieved. Therefore, a device breakdowncan be prevented against a steep voltage change (dv/dt).

Also, because withstand voltage can be increased by the p-type floatingregion that is deeper than the p-type base region, while the p-type baseregion may be shallow, a rise in ON-voltage can also be suppressed byappropriately designing the depth of the p-type base region.

(Section 7) The semiconductor device according to section 6, wherein theoverlap portion has an end portion positioned on a side closer to thegate trench with respect to a center in a width direction of the emittertrench.

According to this arrangement, a collector-emitter voltage to be appliedto the emitter junction trench can be more satisfactorily relieved.

(Section 8) The semiconductor device according to section 2, wherein thesemiconductor device has a trench unit including a pair of the gatetrenches and a dummy trench sandwiched between the pair of gatetrenches.

(Section 9) The semiconductor device according to section 8, wherein thefirst buried electrode is electrically connected with the gateelectrode.

(Section 10) The semiconductor device according to section 9, whereinthe trench unit is formed in plural numbers in a transverse directionalong the front surface of the semiconductor layer, and thesemiconductor device further includes a plurality of emitter trenchesformed between the trench units adjacent to each other, a second buriedelectrode filled via an insulating film in the emitter trench,electrically connected with the n⁺-type emitter region, and a p-typefloating region formed between the plurality of emitter trenches.

(Section 11) The semiconductor device according to section 10, whereinthe p-type floating region is formed deeper than the p-type base region,and includes an overlap portion that goes around to a lower side of theemitter trench.

According to this arrangement, because the p-type floating region(overlap portion) is formed up to a bottom portion of the emitter trenchfilled with the second buried electrode connected to the n⁺-type emitterregion (hereinafter, referred to as an emitter junction trench”), acollector-emitter voltage to be loaded on the emitter junction trench atswitching-off operation can be relieved. Therefore, a device breakdowncan be prevented against a steep voltage change (dv/dt).

Also, because withstand voltage can be increased by the p-type floatingregion that is deeper than the p-type base region, while the p-type baseregion may be shallow, a rise in ON-voltage can also be suppressed byappropriately designing the depth of the p-type base region.

(Section 12) The semiconductor device according to section 11, whereinthe overlap portion has an end portion positioned on a side closer tothe gate trench with respect to a center in a width direction of theemitter trench.

According to this arrangement, a collector-emitter voltage to be appliedto the emitter junction trench can be more satisfactorily relieved.

(Section 13) The semiconductor device according to any one of sections1to 12, wherein the buried insulating film has a thickness of 0.5 μm ormore.

(Section 14) The semiconductor device according to any one of sections 1to 13, wherein the dummy trench is disposed at an interval of 2 μm orless with the gate trench.

(Section 15) The semiconductor device according to any one of sections 1to 14, wherein the n⁺-type emitter region has an n-type dopantconcentration of 1×10¹⁹ cm⁻³ to 5×10²⁰ cm⁻³.

(Section 16) The semiconductor device according to any one of sections 1to 15, wherein the p-type base region has a p-type dopant concentrationof 1×10¹⁶ cm⁻³ to 1×10¹⁸ cm⁻³.

(Section 17) The semiconductor device according to any one of sections 1to 16, wherein the n⁻-type drift region has an n-type dopantconcentration of 1×10¹³ cm⁻³ to 5×10¹⁴ cm⁻³.

(Section 18) The semiconductor device according to any one of sections 1to 17, wherein the p⁺-type collector region has a p-type dopantconcentration of 1×10¹⁵ cm⁻³ to 2×10¹⁹ cm⁻³.

EXAMPLES

Next, the present invention will be described based on examples, but thepresent invention is not limited by the following examples.

A withstand voltage test was performed for four types of devicesmutually different in the interval L₃ between the gate trench 10 and theemitter trench 14, regarding the structure of the semiconductor device 1shown in FIG. 2, in order to demonstrate the effect of an increase inwithstand voltage of the present invention. The result is shown in FIG.16. According to FIG. 16, it could be confirmed that the withstandvoltage is 1472V at a trench interval L₃ of 0.8 μm, and 1456V at 1.35μm, and 1435V at 2 μm, and all are excellent in withstand voltageperformance. On the other hand, the device with a trench interval L₃ of2.8 μm, the withstand voltage of which remained 1320V, is inferior inwithstand voltage performance to the devices with trench intervals L₃ of2 μm or less.

Next, V_(CE)-I_(Cf) characteristics of four types of devices that aremutually different in the interval L₁ between the gate trench 108 andthe dummy trench 109 were examined, regarding the structure of thesemiconductor device 101 shown in FIG. 11, in order to confirm how theeffect to improve the trade-off relationship between the short-circuitcapacity and ON-voltage (V_(CE)) changes depending on said interval L₁.The result is shown in FIG. 17. In FIG. 17, device A (trench intervalL₁=2 μm: alternate long and short dashed line) and device C (trenchinterval L₁=3.5 μm: broken line) are shown.

According to FIG. 17, it could be confirmed that the narrower the trenchinterval L₁, the lower V_(CE)(sat) at rising and the lower steady loss(refer to the lower right enlarged view of FIG. 17). Also, it could beconfirmed that in a high-current range of I_(Cf), the saturation currentdensity has been lowered by trench miniaturization (a reduction involume of the p-type base region 111), and the short-circuit capacityhas been increased.

1. A semiconductor device comprising: a semiconductor layer; a gatetrench formed in the semiconductor layer; a gate electrode filled via agate insulating film in the gate trench; a dummy trench formed spaced ata predetermined interval lateral to the gate trench; an n⁺-type emitterregion, a p-type base region, and an n⁻-type drift region disposed, in aregion between the gate trench and the dummy trench, in order in a depthdirection of the gate trench from a front surface side of thesemiconductor layer; a p⁺-type collector region disposed on a backsurface side of the semiconductor layer with respect to the n⁻-typedrift region; a buried insulating film filled in the dummy trench, theburied insulating portion having an upper surface at a bottom side ofthe dummy trench with respect to the front surface of the semiconductorlayer such that a part of the p-type base region is exposed at a sidesurface of the dummy trench as a contact region; and a contact electrodefilled in a region over the buried insulating film of the dummy trench,connected to the contact region on the side surface of the dummy trench.2. The semiconductor device according to claim 1, wherein thesemiconductor device further includes a first buried electrode filledvia an insulating film in a region under the buried insulating film ofthe dummy trench.
 3. The semiconductor device according to claim 2,having a trench unit including a pair of the dummy trenches and a gatetrench sandwiched between the pair of dummy trenches.
 4. Thesemiconductor device according to claim 3, wherein the first buriedelectrode is electrically connected with the n⁺-type emitter region. 5.The semiconductor device according to claim 4, wherein the trench unitis formed in plural numbers in a transverse direction along the frontsurface of the semiconductor layer, and the semiconductor device furtherincludes a plurality of emitter trenches formed between the trench unitsadjacent to each other, a second buried electrode filled via aninsulating film in the emitter trench, electrically connected with then⁺-type emitter region, and a p-type floating region formed between thedummy trench of the trench unit and the dummy trench of the trench unitnext thereto.
 6. The semiconductor device according to claim 5, whereinthe p-type floating region is formed deeper than the p-type base region,and includes an overlap portion that goes around to a lower side of thedummy trench.
 7. The semiconductor device according to claim 6, whereinthe overlap portion has an end portion positioned on a side closer tothe gate trench with respect to a center in a width direction of theemitter trench.
 8. The semiconductor device according to claim 2, havinga trench unit including a pair of the gate trenches and a dummy trenchsandwiched between the pair of gate trenches.
 9. The semiconductordevice according to claim 8, wherein the first buried electrode iselectrically connected with the gate electrode.
 10. The semiconductordevice according to claim 9, wherein the trench unit is formed in pluralnumbers in a transverse direction along the front surface of thesemiconductor layer, and the semiconductor device further includes aplurality of emitter trenches formed between the trench units adjacentto each other, a second buried electrode filled via an insulating filmin the emitter trench, electrically connected with the n⁺-type emitterregion, and a p-type floating region formed between the plurality ofemitter trenches.
 11. The semiconductor device according to claim 10,wherein the p-type floating region is formed deeper than the p-type baseregion, and includes an overlap portion that goes around to a lower sideof the emitter trench.
 12. The semiconductor device according to claim11, wherein the overlap portion has an end portion positioned on a sidecloser to the gate trench with respect to a center in a width directionof the emitter trench.
 13. The semiconductor device according to claim1, wherein the buried insulating film has a thickness of 0.5 μm or more.14. The semiconductor device according to claim 1, wherein the dummytrench is disposed at an interval of 2 μm or less with the gate trench.15. The semiconductor device according to claim 1, wherein the n⁺-typeemitter region has an n-type dopant concentration of 1×10¹⁹ cm⁻³ to5×10²⁰ cm⁻³.
 16. The semiconductor device according to claim 1, whereinthe p-type base region has a p-type dopant concentration of 1×10¹⁶ cm⁻³to 1×10¹⁸ cm⁻³.
 17. The semiconductor device according to claim 1,wherein the n⁻-type drift region has an n-type dopant concentration of1×10¹⁵ cm⁻³ to 5×10¹⁴ cm⁻³.
 18. The semiconductor device according toclaim 1, wherein the p⁺-type collector region has a p-type dopantconcentration of 1×10¹⁵ cm⁻³ to 2×10¹⁹ cm⁻³.